US2064608A - Cellulose derivative coating composition - Google Patents

Description

Patented Dec. 15, 1936 outcomes nnnrva'rrvn ooa're' conrosrrron norm 'ry'lelnecks,

South River, N. 5., assignor to E. I. du Pontde Ncmours dz (lompany, Wilton, llet, a corporation of Delaware No Drawing. Application July Z, 1934, Serial No. 734,211

'Cl.- (Q1. 130-79) This invention relates to a decorative and protective coating composition for use on electrical equipment and more particularly to a decorative and protective coating composition having high insulating properties, high dielectric strength and high resistance to so-c'alled arc trailing.

In the finishing of electric switch boards, insulated wires and other similar equipment which is used in connection with high tension electric currents, it is necessary to use decorative or protective coating compositions which in themselves have high insulating properties, high dielectric strength and high resistance to so-called .arc trailing. Arc trailing is a property possessed by some surfaces of readily supporting an electric are over any area where an arc has previously been formed. Resistance to this farc trailing is of particular importance in surface coatings for switch boards and it is frequently desirable that such coating-compositions possess decorative value, for example, hiding power, as well as protective properties. Soluble clack dyes have been incorporated in the compositions for such purposes in amounts sufiicient to produce opaque or nearly opaque finished film. use of such soluble black dyes has two definite disadvantages. First, the composition containing" the dyes cannot be made suficiently opaque an less an excessive amount of the dye is used, and, second, the resultant finish, has too high a luster. Black pigments such as lamp black, carbon black, bone black, which are commonly used in coating compositions to produce high hiding power, reduce the insulating properties, dielectric strength and resistance to arc trailing" to such an extent that their use is unsatisfactory for the purpose of the invention. It is highly desirable for most electrical equipmentv used in connection with high tension currents, particularly switch boards, to have a matte finish rather than a high luster finish.

This invention has as an object the production of opaque coating compositions which will produce a film possessing high insulating properties and high dielectric strength. A further object is the production of a coating composition which, in addition to producing a film of satisfactory insulating properties, dielectric strength and opaqueness, will also produce a film which has a matte finish. A further object is the production of a surface coating having high resistance to arc trailing.

These objects are accomplished in the present invention by the provision of a composition in which manganese dioxide in a finely divided con- 'dition, is dispersed in a coating'composition, the

ingredients of such coating composition beingselected so that there will be no reducing action upon the highly reactive manganese dioxide either during storage of the composition or in the dried film deposited from such acomposition.

The invention is best exemplified by the following examples of compositions whichare given as illustrations, and not by way of limitation:

50% solution of dewaxedshellacjln ethyl alcohol lid Butyl alcohol 5.0 Denatured alcohol 6.5 Ethyl acetate 3.0 Butyl acetate 13.0 Toluene 3.0

trample El Per cent Manganese dioxide 12.0 Nlgrosine m- 0.8 lllihutyl phthalate s 3.6 Castor oil 2.3 nitrocellulose 11.0 44% dammar solution 0.3 Butyl alcohol 3.0 Denatured alcohol 9.0 Ethyl acetate 20.0 Pentaso acetate 0.0 Toluene 7.0 Solvent naphtha 15.0 Butyl acetate 3.0

Example III Per cent Manganese dioxide 20.0 Tricresyl phosphate 3.0 Condensation product of para toluene sulphamide and formaldehyde .f--- 5.0 Cellulose acetate .4. 8.0 Diacetone alcohol 26.0 Methyl alcohol 12.0. Acetone 6.0 Mono methyl ether of ethylene glycol.. 20.0

'the cellulose derivative in the solvent media and adding the other ingredients according to procedures well known in the art. .Suitable variations can be incorporated without departing from the spirit of the invention and such variations will be readily apparent-to those skilled in the art. The nigrosine in Example II is a soluble blackdye which may be used to impart a more pleasing appearance to the finished product. However, its use is optional.

In preparing the compositions of the inven-' tion, it is important to avoid the introduction of any material which will'have a tendency-to reduce the manganese dioxide or on which conversely the manganese dioxide will have an oxidizing effect either by direct oxidation or by catalytic means. Drying, oils, for examplefshould be especially avoided, since manganese salts are well known siccatives for such materials. It is apparent, therefore, that ordinary paint vehicles are unsatisfactory.

Other cellulose derivatives than those mentioned in the examples, such as cellulose ether, for, example ethyl cellulose and benzyl cellulose can be satisfactorily used. In the preparation of such compositions the choice of solvents is wide and will be readily apparent to those skilled in the art. The use of gums or resins, either natural or synthetic, also offers a rather wide range of choice.

In the above examples the. manganese dioxide varies from 12% to B7%%. The preferred range is usually from 10% to.50%. However, I do not want to be limited to the exact range, since for certain purposes I may use even less than 10% and fol-other purposes even more than 50%, as

will be evident to those skilled in the art. H

The composition of the invention is particularly adaptable for use on electrical equipment for decorative and protective purposes such as switch boards, electric conduits, cables, transformers, generators, electric recording devices,

. etc. It finds use also for other articles where a 45- protective and decorative coating composition having the desirable properties possessed by the composition of the invention is desired or necessary.

The invention presents as advantages over the present state of the art, the fact that the com-.

position produces an opaque film having high insulating properties and high dielectric strength. Further, the composition produces an opaque film having the desired matte finish without impairing the n electrical properties. A

further advantage is the production ofa decorative and protective coating which a high resistance to are trailing, a highly desirable property in coating compositions'used on certain types of electrical equipment.

It is apparent that many widely diiferent embodiments of this invention may be made without departing from the spirit and scope thereof and, therefore, it is not intended to be limited ,except as indicated by the appended claims.

I claim: 1. In the process of preparing odlulos'e deriyative coating compositions of high dielectric strength, the step of adding from 10 to 50% hi weightof finely divided i dioxide. 2. A coating composition comprising 'a eellu lose derivative, a softener, a resin, and 10 to 50% of finely divided manganese dioxide. 1

3. The composition ot'claim 2, in which the cellulose derivative is cellulose acetate..

\ '4. The coating composition of claim 2. in which the cellulose derivative is cellulose nitrate.

5.'A coating composition comprising acellulose derivative, a softener, a resin, and from 10 to 50% by weight of finely divided dioxide. v l V 6. A coating composition of high dielectric strength containingapproximately the following formula by weight:

Percent Manganese dioxide 37.5 Dibutyl phtha 2.0 Castor oil--- V 1.0 nitrocellulose 9.0 50% solution of dewaxed shellac in ethyl alcohol- 20.0 Butyl alcohol 5.0 Denatured alcohol 6.5 Ethyl acetate 3.0 Butyl acetat 13.0 Toluene -3.0

'I. A coating composition of high dielectric strength containing approximately 'the following and from 10 to of manganese dioxide. 9. The coating composition of claim 8 which includes a resin.

10. The coating composition-of claim 8 which includes a softener.

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